Domestic cats kill billions of animals every year, prompting scientists to worry about the effects on wildlife populations. While much of the damage is inflicted by cats without owners, such as strays, pet cats also contribute to the toll. Reining in these zealous predators requires help from pet owners — but a new study suggests that getting their cooperation won’t be easy.

To cat lovers, their pets’ behavior may seem harmless. If each cat kills a couple of birds or mice per month, what’s the big deal? The problem is the sheer number of cats. There are more than 10 million pet cats in the UK and an estimated 84 million in the United States. Since these creatures are coddled and fed at home, their numbers are far higher than they would be if the cats had to fend for themselves in the wild.

A team of UK researchers wanted to find out if owners understood the extent and impact of their pets’ hunting. “A naive hypothesis would be that owners of highly predatory cats are more likely to agree that cats are harmful to wildlife,” the team writes. “However,” they add, “any attachment between owner and cat might defy any decision-making based upon ecological rationale.”

To investigate, the researchers recruited pet owners in the villages of Mawnan Smith, England and Thornhill, Scotland. The participants answered surveys about cat predation and recorded the number of dead animals that their cats brought home. The final study included 86 cats, tracked for four months in Mawnan Smith and for 14 months in Thornhill.

Mawnan Smith cats nabbed an average of about two animals per month, while those in Thornhill averaged about one per month. The most active hunter brought home about 10 animals per month. The prey included mice, shrews, voles, and birds, mostly from native species.

In general, owners were able to predict whether their cat would bring home any prey at all. But they didn’t accurately estimate how many animals their pets would kill. And owners of the most avid hunters were not more likely to agree that cats harmed wildlife or that cats should be kept inside at night. Some owners appeared to be so irritated with the survey that they added comments such as “but it’s nature” and “some wildlife is harmful to cats”. The only control measure that the majority of owners approved of was sterilization.

Instead of trying to convince owners that their cats could harm other species, the authors say, managers may need to argue that control strategies benefit the cats themselves. For example, cats that spend more time inside are less likely to be hit by cars, get injured in fights, catch diseases, or accidentally ingest poison. — Roberta Kwok | 2 July 2015